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An image forming apparatus including: a first charging device for charging
an imageable surface; recording means for recording an electrostatic
latent image on the imageable surface; developing means for developing
the electrostatic latent image with developer; a second charging device
for transferring a developer image on the imageable surface onto an a
substrate; control means for setting a value of the bias of either the
first charging device or the second charging device from an operating
bias to a testing bias; test pattern forming means for forming test
patterns on the imageable surface at operating bias and said testing
bias; test patterns detection means for scanning non-uniformity of the
test patterns, and means for associating non-uniformity of the test
patterns to a reliability condition of either the first charging device
and/or second charging device.

1. A system for sensing a reliability condition of a charging device,
comprising:an imageable surface, charging said imageable surface with the
charging device;a controller for setting a value of the operating bias of
the charging device based upon formation of a normal image to a testing
bias;means for recording an electrostatic latent image of a test pattern
on an imageable surface at said testing bias;means for developing the
electrostatic latent image of the test pattern with developer;means for
scanning the non-uniformity of the test pattern,means for quantifying the
non-uniformity of the test pattern; andmeans for associating the
non-uniformity of the test pattern to a reliability condition value of
the charging device.

2. The system of claim 1, wherein said value of the operating bias upon
formation of the normal image is substantially different from the value
of the testing bias upon formation of the test pattern.

3. The system of claim 1, wherein said test patterns scanning means
includes an optical array or scanbar sensor for measurement of toner mass
on a substrate.

4. The system of claim 3, wherein said substrate includes one or more
selected from the group consisting of a photoconductor surface, an
intermediate transfer member, and a paper substrate.

5. The system of claim 3, wherein said optical array sensor extends along
the full process width of said substrate.

6. The system of claim 1, further including means for cleaning said
charging device.

7. The system of claim 1, wherein said associating means generates a feed
back signal to enable adjustment of said cleaning means.

8. The system of claim 1, wherein said associating means generates a feed
back signal that corresponds to the reliability condition of said
charging device.

9. The system of claim 8, wherein said feedback signal includes an
estimated number of cycles left in the useable life of the charge device.

10. The system of claim 8, wherein said feedback signal is provided to a
user interface for user or service technician use.

11. The system of claim 8, wherein said feedback signal is provided to a
remote diagnostics application.

12. A method for sensing a reliability condition of a charging device,
comprisingcharging an imageable surface with the charging device; said
charging includes setting a value of the bias of the charging device from
an operating bias to a testing bias;recording an electrostatic latent
image of a test pattern on an imageable surface;developing the
electrostatic latent image of the test pattern with developer;scanning
non-uniformity of the developed latent image of the test
pattern,determining a non-uniformity state of the developed latent image;
andassociating the non-uniformity state to a reliability condition value
of the charging device.

13. The method of claim 12, wherein the testing bias upon formation of the
test pattern is substantially different from the operating bias value for
the formation of a normal image.

14. The method of claim 12, wherein said scanning includes measuring toner
mass on a substrate.

15. The method of claim 12, wherein said scanning includes scanning one or
more selected from the group consisting of a photoconductor surface, an
intermediate transfer member, and a paper substrate.

16. The method of claim 12, further including cleaning the charging device
in response to the reliability condition.

17. The method of claim 12, wherein said associating includes generating a
feed back signal to enable adjustment of said cleaning.

[0002]This invention relates generally to a charge generating device, and
more particularly concerns a method and apparatus for cleaning a charging
device.

[0003]In a typical electrophotographic printing process, a photoconductive
member is charged to a substantially uniform potential so as to sensitize
the surface thereof. The charged portion of the photoconductive member is
exposed to a light image of an original document being reproduced.
Exposure of the charged photoconductive member selectively dissipates the
charges thereon in the irradiated areas. This records an electrostatic
latent image on the photoconductive member corresponding to the
informational areas contained within the original document. After the
electrostatic latent image is recorded on the photoconductive member, the
latent image is developed by bringing a developer material into contact
therewith.

[0004]Generally, the developer material comprises toner particles adhering
triboelectrically to carrier granules. The toner particles are attracted
from the carrier granules to the latent image forming a toner powder
image on the photoconductive member. The toner powder image is then
transferred from the photoconductive member to a copy sheet. The toner
particles are heated to permanently affix the powder image to the copy
sheet. In printing machines such as those described above, corona devices
can be used to perform a variety of functions in the printing process.

[0005]For example, corona devices aid the transfer of the developed toner
image from a photoconductive member to a transfer member. Likewise,
corona devices aid the conditioning of the photoconductive member prior
to, during, and after deposition of developer material thereon to improve
the quality of the electrophotographic copy produced thereby. Both direct
current (DC) and alternating current (AC) type corona devices are used to
perform these functions. One form of a corona charging device comprises a
corona electrode in the form of an elongated wire connected to a high
voltage AC/DC power supply. Alternatively, a charging device may comprise
an array of pins integrally formed from a sheet metal member. Another
alternative charging device is a biased charge roll (BCR) type device.

[0006]The scorotron is similar to the pin corotron, but is additionally
provided with a screen or control grid disposed between the coronode and
the photoconductive member. The screen is held at a lower potential
approximating the charge level to be placed on the photoconductive
member. The scorotron provides for more uniform charging and prevents
overcharging.

[0007]A problem with electrophotographic printing process is the
accumulation of silica and other contamination on the corona electrode.
These accumulations are adhered onto the corona electrode due to the high
voltage placed on the corona electrode during operation. These
accumulations can deteriorate the image quality and can interrupt the
continuous use of these printers by causing print defects, such as dark
streaks on the printed pages. For some cases, these defects could be
cured by simply wiping the contamination from the small thin corona
electrode. Similar accumulation can occur on the surface of a BCR
generating similar problems.

[0008]Unfortunately the rate of charger contamination, and the build-up of
the associated non-uniformity in the output prints, is not presently easy
to measure. As a result, contamination related failures are highly
unpredictable and can vary greatly from one machine to another. Thus,
unscheduled maintenance events (UMs) due to charger contamination are
still fairly common. In an attempt to decrease the number of UMs, service
technicians will often change the charge device, prior to its actual end
of life, while servicing the machine for other reasons to prevent having
to return for a charger UM event at a later time. Both UM events and the
replacement of charge devices prior to their end of life result in
increased system run cost. A method for measuring the actual
contamination state of the charge device, and perhaps for predicting the
future onset of contamination related PQ streaks, could help to improve
system run costs.

[0009]Additionally, in many cases the charge device cleaner can actually
have negative impacts on the function of the charge device itself over
time. For instance, in biased charge roll (BCR) systems the cleaning
device can often lead to abrasion of the surface of the BCR. This
abrasion then results in the onset of dark streaks print quality (PQ)
failures in the output prints. The difficulty lies in designing a cleaner
for the charging device that is aggressive enough to remove the unwanted
contamination and films (thereby sufficiently extending the life of the
charger) while not being so aggressive as to cause unwanted impacts to
the charger (e.g. abrasion). This is a difficult balance to optimize
particularly when some of the free parameters are fixed at design time
(e.g. the force applied to the cleaning device). FIG. 1 is a model that
illustrates the required design tradeoff for a BCR charge device cleaner.
The difficulties associated with this tradeoff are further exacerbated by
the fact that the contamination level of the charge device can be
significantly impacted by a variety of factors: temperature and relative
humidity, age of the devices, air flow, availability of contaminants,
etc. Similarly, it is difficult to predict the likelihood of damage to
the charge device for a given cleaning action as there are a variety of
noise factors which affect this as well.

[0010]The present disclosure obviates the problems noted above by
providing a method for detecting and measuring charge device
contamination levels prior to the critical threshold that would result in
print quality streaks in the output customer prints. By operating the
charge device in a much more stressful (less robust) mode during a test
mode, the degree of streaks due to charger contamination can actually be
enhanced. By appropriate sensing, the contamination level of the charge
device can therefore be measured/characterized prior to the onset of PQ
defects (streaks) in the output customer prints. Such information could
then be used to drive a variety of service or process control related
actions, thereby improving overall system run cost.

SUMMARY OF THE INVENTION

[0011]There is provided an image forming apparatus including a first
charging device for charging an imageable surface; recording means for
recording an electrostatic latent image on said imageable surface;
developing means for developing the electrostatic latent image with
developer; a second charging device for transferring a developer image on
the imageable surface onto a substrate; control means for setting a value
of the bias of either said first charging device or said second charging
device from an operating bias to a testing bias; test pattern forming
means for forming test patterns on the imageable surface at operating
bias and said testing bias; test patterns detection means for scanning
non-uniformity of the test patterns, and means for associating
non-uniformity of the test patterns to a reliability condition of either
said first charging device and/or second charging device

[0012]Other features of the present invention will become apparent as the
following description proceeds and upon reference to the drawings, in
which:

[0013]FIG. 1 is a model that illustrates design tradeoffs for a BCR charge
device cleaner;

[0015]FIG. 3 is a schematic view illustrating a charging device with the
cleaning device of the present disclosure;

[0016]FIG. 4 is a schematic view illustrating another embodiment of the
charging device with the cleaning device of the present disclosure;

[0017]FIG. 5 illustrates a comparison of non-uniformity profiles for
sample prints made under operating bias and test bias; and

[0018]FIGS. 6-8 are flow diagrams illustrating possible operation of the
cleaning system of the present disclosure.

[0019]While the present disclosure will be described in connection with a
preferred embodiment thereof, it will be understood that it is not
intended to limit the disclosure to that embodiment. On the contrary, it
is intended to cover all alternatives, modifications, and equivalents as
may be included within the spirit and scope of the disclosure as defined
by the appended claims.

[0020]For a general understanding of the features of the present
disclosure, reference is made to the drawings. In the drawings, like
reference numerals have been used throughout to identify identical
elements.

[0021]FIG. 2 schematically depicts an electrophotographic printing machine
incorporating the features of the present disclosure therein. It will
become evident from the following discussion that the present invention
may be employed in a wide variety of devices and is not specifically
limited in its application to the particular embodiment depicted herein.

[0022]Referring to FIG. 2 of the drawings, an original document is
positioned in a document handler 27 on a raster input scanner (RIS)
indicated generally by reference numeral 28. The RIS contains document
illumination lamps, optics, a mechanical scanning drive and a charge
coupled device (CCD) array. The RIS captures the entire original document
and converts it to a series of raster scan lines. This information is
transmitted to an electronic subsystem (ESS) which controls a raster
output scanner (ROS) described below. FIG. 2 schematically illustrates an
electrophotographic printing machine which generally employs a
photoconductive belt 10. Preferably, the photoconductive belt 10 is made
from a photoconductive material coated on a ground layer, which, in turn,
is coated on an anti-curl backing layer. Photoconductive belt 10 moves in
the direction of arrow 13 to advance successive portions sequentially
through the various processing stations disposed about the path of
movement thereof. Photoconductive belt 10 is entrained about stripping
roller 14, tensioning roller 20 and drive roller 16. As drive roller 16
rotates, it advances photoconductive belt 10 in the direction of arrow
13. Initially, a portion of the photoconductive surface passes through
charging station A.

[0023]At charging station A, a corona generating device indicated
generally by the reference numeral 22 charges the photoconductive belt 10
to a relatively high, substantially uniform potential. At an exposure
station, B, a controller or electronic subsystem (ESS), indicated
generally by reference numeral 29, receives the image signals
representing the desired output image and processes these signals to
convert them to a continuous tone or grayscale rendition of the image
which is transmitted to a modulated output generator, for example the
raster output scanner (ROS), indicated generally by reference numeral 30.
Preferably, ESS 29 is a self-contained, dedicated minicomputer. The image
signals transmitted to ESS 29 may originate from a RIS as described above
or from a computer, thereby enabling the electrophotographic printing
machine to serve as a remotely located printer for one or more computers.
Alternatively, the printer may serve as a dedicated printer for a
high-speed computer. The signals from ESS 29, corresponding to the
continuous tone image desired to be reproduced by the printing machine,
are transmitted to ROS 30. ROS 30 includes a laser with rotating polygon
mirror blocks.

[0024]The ROS will expose the photoconductive belt to record an
electrostatic latent image thereon corresponding to the continuous tone
image received from ESS 29. As an alternative, ROS 30 may employ a linear
array of light emitting diodes (LEDs) arranged to illuminate the charged
portion of photoconductive belt 10 on a raster-by-raster basis. After the
electrostatic latent image has been recorded on photoconductive substrate
12, belt 10 advances the latent image to a development station, C, where
toner, in the form of liquid or dry particles, is electrostatically
attracted to the latent image using commonly known techniques.

[0026]With continued reference to FIG. 2, after the electrostatic latent
image is developed, the toner powder image present on photoconductive
belt 10 advances to transfer station D. A print sheet 48 is advanced to
the transfer station, D, by a sheet feeding apparatus, 50. Preferably,
sheet feeding apparatus 50 includes a nudger roll 51 which feeds the
uppermost sheet of stack 54 to nip 55 formed by feed roll 52 and retard
roll 53. Feed roll 52 rotates to advance the sheet from stack 54 into
vertical transport 56.

[0027]Vertical transport 56 directs the advancing sheet 48 of support
material into the registration transport 120, past image transfer station
D to receive an image from photoreceptor belt 10 in a timed sequence so
that the toner powder image formed thereon contacts the advancing sheet
48 at transfer station D. Transfer station D includes a corona generating
device 58 which sprays ions onto the back side of sheet 48. This attracts
the toner powder image from photoconductive substrate 12 to sheet 48. The
sheet is then detacked from the photoreceptor by corona generating device
59 which sprays oppositely charged ions onto the back side of sheet 48 to
assist in removing the sheet from the photoreceptor. After transfer,
sheet 48 continues to move in the direction of arrow 60 by way of belt
transport 62 which advances sheet 48 to fusing station F.

[0028]Fusing station F includes a fuser assembly indicated generally by
the reference numeral 70 which permanently affixes the transferred toner
powder image to the copy sheet. Preferably, fuser assembly 70 includes a
heated fuser roller 72 and a pressure roller 74 with the powder image on
the copy sheet contacting fuser roller 72. The pressure roller is cammed
against the fuser roller 72 to provide the necessary pressure to fix the
toner powder image to the copy sheet. The fuser roller is internally
heated by a quartz lamp (not shown). Release agent, stored in a reservoir
(not shown), is pumped to a metering roll (not shown). A trim blade (not
shown) trims off the excess release agent. The release agent transfers to
a donor roll (not shown) and then to the fuser roller 72. The sheet then
passes through fuser assembly 70 where the image is permanently fixed or
fused to the sheet. After passing through fuser 70, a gate 80 either
allows the sheet to move directly via output 84 to a finisher or stacker,
or deflects the sheet into the duplex path 100, specifically, first into
single sheet inverter 82. That is, if the sheet is either a simplex
sheet, or a completed duplex sheet having both side one and side two
images formed thereon, the sheet will be conveyed via gate 80 directly to
output 84.

[0029]Scanning of test patterns can be on accomplished by scanning the
sheet. Test pattern scanner 85 scans selected sheets having test patterns
thereon. The selected sheets have test patterns thereon are conveyed via
gate 80 directly to output 84. Alternatively, scanning of test patterns
can be accomplished by scanning the developed test pattern on the
photoconductive substrate prior to transfer with test pattern scanner 86.
Test pattern scanners 85 and 86 includes an optical array or scanbar
sensor adapted to measure toner mass on various substrates, preferably
the optical array sensor extends along the full process width of the
image forming apparatus. The scanned image data is sent to controller 29
whereupon the scanned image is analyzed for uniformity.

[0030]However, if the sheet is being duplexed and is then only printed
with a side one image, the gate 80 will be positioned to deflect that
sheet into the inverter 82 and into the duplex path 100, where that sheet
will be inverted and then fed to acceleration nip 102 and belt transports
110, for recirculation back through transfer station D and fuser 70 for
receiving and permanently fixing the side two image to the backside of
that duplex sheet, before it exits via exit path 84. After the print
sheet is separated from photoconductive substrate 12 of photoconductive
belt 10, the residual toner/developer and paper fiber particles adhering
to photoconductive substrate 12 are removed therefrom at cleaning station
E.

[0031]Cleaning station E includes a rotatably mounted fibrous brush in
contact with photoconductive substrate 12 to disturb and remove paper
fibers and a cleaning blade to remove the nontransferred toner particles.
The blade may be configured in either a wiper or doctor position
depending on the application. Subsequent to cleaning, a discharge lamp
(not shown) floods photoconductive substrate 12 with light to dissipate
any residual electrostatic charge remaining thereon prior to the charging
thereof for the next successive imaging cycle.

[0032]The various machine functions are regulated by controller 29. The
controller is preferably a programmable microprocessor which controls all
of the machine functions hereinbefore described. The controller 29
provides a comparison count of the copy sheets, the number of documents
being recirculated, the number of copy sheets selected by the operator,
time delays, jam corrections, etc. Conventional sheet path sensors or
switches may be utilized to keep track of the position of the document
and the copy sheets.

[0033]Turning next to FIG. 3, focusing on an embodiment of a charging
device with cleaning device of the present disclosure, as illustrated the
grid 310 is installed in the frame 304. Frame 304 has a groove which
supports grid 310 therein. Wire 312 is positioned below grid 310. The
charging devices include end blocks, which support wire 312. The cleaning
device of the present disclosure employs annular cleaning pads for the
grid and the grid side of the wire. Both cleaning pads are mounted on a
circular base with a mechanism to rotate the base a fraction of a turn
each time the cleaner returns to the home position. For example one
design rotates the pads by 45.degree. with each cleaning cycle. In this
case, the wire and grid are each effectively cleaned by eight different
cleaning pads. If each of the eight orientations cleans a few strips of
the wire, the various strips will overlap so that over time, the entire
wire will be cleaned thoroughly.

[0034]Cleaning device 315 is driven along the inner portion of charging
device by a lead screw 314 being rotated by motor 400. Cleaning device
315 has a scrub pad 330 on the top surface thereof for cleaning any
particles (ie toner or debris) adhering to grid 310 as the cleaning
device moves along the charging device. Wire cleaning pads remove any
particles (i.e., silica or debris) adhering to wire 312 as the cleaning
carriage moves along the charging device Cleaning device 315 is
controlled by controller 402, the operation of which will be described
infra.

[0035]FIG. 4 illustrates another embodiment of a charging device with a
cleaning device of the present disclosure. This embodiment features a
bias charge roll 200. In various exemplary embodiments, the bias charge
roll 200 comprises a charging member 213 disposed opposite to the surface
of the movable charged body, that is, the surface of the photoconductive
substrate 12 in the exemplary embodiment shown, and a power source 214
that applies a voltage to the charging member 213. A voltage is applied
to the charging member 213 by this power source 214 to produce electric
discharge between the charging member 213 and the surface of the
photoconductive substrate 12, and the surface of the photoconductive
substrate 12 is charged to a predetermined polarity.

[0036]The charging member 213 is structured in any of various types as
explained later. The exemplary charging member 213 shown in FIG. 4 is
cylindrically formed, with the shaft made of metal such as stainless
steel and the outer layer is made of a conductive elastomer. When
charging the charged body, the charging member 213 is, in various
exemplary embodiments, positioned in a non-contact state with respect to
the surface of the charged body. In other exemplary embodiments, the
charging member is positioned in contact with the surface of the charged
body. The exemplary charging member 213 shown in FIG. 4 is disposed in
contact with the photoconductive substrate 12. Cleaning device 215 has a
scrub pad 230 for cleaning any particles (i.e., toner or debris) adhering
to the BCR as the cleaning device engages into contact with the charging
device via cam assembly 229. In some embodiments, the scrub pad 230 may
be a stationary foam pad or fibrous brush. In alternate embodiments, this
device may be a foam roller. The engagement of cam assembly 229 is
controlled by controller 402, the operation of which will be described
infra.

[0037]In normal operation of the BCR, a voltage obtained by superimposing
an AC voltage on a DC voltage is applied to the charging member 213, and
the photoconductive substrate 12 is charged to the same potential as the
applied DC voltage. In various exemplary embodiments the superimposed
voltage of the DC voltage and the AC voltage is applied to the charging
member 213 to produce electric discharge between the charging member 213
and the surface of the charged body, and charge is applied to the charged
body. As explained above, by applying not only the DC voltage but also
the AC voltage, in various exemplary embodiments the charge uniformity on
the surface of the photoconductive substrate 12 is increased.

[0038]Applicants have found that most charging systems are designed to
operate in a fairly robust region of the actuator latitude space. For
example, most BCR chargers for color engines are operated in AC mode with
fairly substantial peak-to-peak voltages. This assists in ensuring that
the photoreceptor (P/R) is charged to a fairly uniform level despite
reasonably wide variations in operating parameters (environment,
contamination of the BCR, etc). Instead of operating the charge device in
its designed, robust regime, it is possible to instead operate the device
at a more stressful (less robust) set of actuator settings during a
diagnostic/sensing mode. For example, for an AC BCR this would involve
operating the device in DC-only mode (or at least at a substantially
reduced AC peak-to-peak voltage). At these less robust settings, the
charge voltage on the P/R coming out of the BCR nip will be much more
susceptible to the state of contamination or abrasion of the charger.
Therefore, the associated print defect level can actually be enhanced by
operating the device in this fashion.

[0039]By printing test patterns while operating the charging device in
this diagnostic (less robust) mode of operation, it is possible to
enhance the amplitude of the print quality artifacts/defects related to
the state of the charging device. The test patterns used in this less
robust mode of operation are typically chosen to further enhance the
potential defects. In an exemplary embodiment, these test patterns would
be mid-range halftones (e.g. 50% area coverage) for each of the
individual color separations. This set of test patterns typically
provides high sensitivity to the types of artifacts (e.g. streaks) that
are related to the contamination/abrasion state of the charge device. By
using a test pattern scanning sensor, e.g. 85 or 86, it is possible to
capture images of the mass structure. These images can then be analyzed
by the controller 29 to extract various features and/or measurements of
the non-uniformity structure.

[0040]The analysis of the captured images can be conducted using a number
of different methods. In an exemplary embodiment, the mean of the image
in the process direction is calculated to produce an inboard-outboard
non-uniformity profile. This profile is then analyzed to identify large
amplitude spikes. In general, these large amplitude spikes in the
uniformity profile correspond to streak defects in the prints. FIG. 5
shows comparisons of non-uniformity profiles (inboard/outboard) for
sample prints made under nominal (BCR AC.apprxeq.1800Vpp) and reduced
(BCR AC.apprxeq.1300Vpp) BCR settings in a printer as the type of FIG. 2.
The results shown are in units of scanner reflectance and the profile
means have been removed to show only the deltas from the means. Note the
downward spikes in these uniformity profiles which indicate various
levels of dark streaks in the associated prints. For the scans under
reduced charger actuator settings, the amplitudes of the spikes have been
substantially increased over those at nominal actuator settings. This can
also be visually observed in the output prints under both operating
conditions. Applicants have observed that under certain charge device
contamination/abrasion conditions, the vertical dark streaks in the print
at nominal actuator settings are barely detectable. However, these
streaks become prominently visible under reduced actuator settings.
Experimental data has shown that streaks that have not yet become visible
in the prints at nominal actuator settings are easily seen at reduced
(less robust) charger settings. Thus, through the sensing method the
amplitudes of the streak levels can be significantly increased during
sensing, thereby greatly improving the ability to accurately measure the
charger contamination profile (i.e., the "contamination state" of the
charge device).

[0041]Having in mind the construction and the arrangement of the principal
elements thereof, it is believed that a complete understanding may now be
had from a description of its operation. During the charging device
testing mode: controller 402 sets a value of the bias of either charging
device 22 or transfer charging devices 58 and 59 from an operating bias
to a testing bias. The value of the operating bias upon formation of a
normal image is substantially different from a value of the testing bias
upon formation of the test pattern. The test pattern is formed and
developed via ESS 29 and ROS 30 on the photoconductive substrate 12. Test
patterns are formed at the operating bias and the testing bias. The test
patterns are scanned for non-uniformity by image sensor 86 adjacent to
the photoconductive substrate 12, or transferred to a substrate and
scanned for non-uniformity by image sensor 85 or document scanner 28.

[0042]In one embodiment, the ESS 29 processes the scanned test patterns
and associates a non-uniformity value to the test patterns. This
non-uniformity value is then treated as representative of the reliability
condition of the charging device. If the non-uniformity value exceeds a
predefined threshold value a feed back signal is generated to enable
cleaning system 215 to clean the charging device. In another embodiment,
the feed back signal is sent to user interface (not shown) or to a remote
site to notify the user or service personnel of the condition or need of
replacement of the charging device.

[0043]The defect enhancement is done employing a test patch preferably in
an inter-document zone to enable early detection of impending failure
modes. Measurements of the enhanced defect level could be made through an
in-situ full-width array (FWA) optical sensor, or through an offline
flatbed scanner. Simple approaches could even make use of visual
interpretation of test prints by a service technician during a diagnostic
mode to determine whether failure of the charger was imminent. Once
again, the non-uniformity profile is substantially enhanced through the
proposed sensing method, thereby making any of the proposed sensors more
effective.

[0044]The sensing method enables early detection of impending charger
failure. In its simplest form, this type of information can be used by a
service representative to determine the expected remaining life of a
charging device (without having to wait for charging related streaks
failures to occur in the customer prints). In more advanced
implementations remote diagnostics applications can be utilized to enable
the machine to periodically make such measurements in an automated
fashion thereby determining the health state of the charge device. This
information can then be used to flag the customer (or service
representative) for re-order of a new charge device (prior to actual
onset of PQ failure). This prevents machine downtime, unscheduled service
calls, and/or wasted prints for charge devices that start to fail in the
middle of long customer jobs.

[0045]As earlier noted by the applicants, a typical engagement of the
charger cleaning device is based upon such things as print count or pixel
count. Applicants have found that there can be a great deal of
variability in the amount of charger contamination that actually occurs.
In addition, it is often the case that the charger cleaning device can
impart damage to the charger over time. For instance, in BCR applications
the BCR cleaner has been observed to cause abrasion of the surface of the
BCR that results in dark streaks print failures in the prints. In fact,
under some operating conditions these abrasion-related streaks onset well
before contamination related streaks would without any charger cleaner
installed in the system. Thus, in some cases the charger cleaning device
can actually shorten the useable life of the overall charging subsystem.

[0046]Applicants have found that prior methods to deal with these issues
are improved BCR materials that are more resistant to contamination and
abrasion, improved BCR cleaner devices, and improvements in the
prediction methods for estimating the actual contamination state of the
charger. However, hardware and materials related approaches can be
problematic/difficult due to design constraints and the difficulties
associated with identifying/sourcing materials with the desired
properties. Estimation based approaches (feed-forward) are difficult
since it is troublesome to accurately predict the rate of contamination
and/or the contamination state of the charger under all operating
conditions and environments.

[0047]A desirable factor of the present disclosure is that it has a
feedback based approach to keep the charge device clean with minimal
negative impacts. In other words, a system which would measure the actual
contamination level, or contamination state, of the charge device and
take appropriate action to maintain an acceptable level of contamination
without imparting unnecessary stress on the charge device itself.

[0048]An embodiment of the invention provides a feedback based approach to
the operation of the charging subsystem's cleaning device in a
xerographic print engine. Rather than estimating the contamination level
of the charger, the actual contamination state is measured and used to
determine the appropriate corrective action. This set of possible
corrective actions would include adjusting the charge device cleaning
rate, adjusting the aggressiveness of the charge device cleaner,
increasing the frequency of the charge device cleaning cycles, etc.
Utilizing the proposed feedback approach, the life of the charging system
could be optimized while maintaining acceptable output print quality
(i.e. no print streaks).

[0049]FIG. 6 illustrates a flow chart wherein a controller periodically
measures the charge device non-uniformity level. When the level is
unacceptably high the controller engages the charge device cleaner for a
fixed duration. Step 300 indicates the start of the process; next at step
310 is the reset print cycle count; at step 320 is the Increment print
cycle count.

[0050]At step 330 the print cycle count is compared to the cycle count
threshold; if the print count is not greater than the cycle count
threshold the process returns to step 320; if the print count is greater
than the cycle count threshold the process goes to step 340 wherein the
test pattern is printed under adjusted charger settings; at step 350 the
test pattern is measured with an image-based sensor; at step 360 the
charge device non-uniformity is calculated.

[0051]At step 370 the charge device non-uniformity is compared to the
non-uniformity threshold; if the charge device non-uniformity is not
greater than the threshold the process goes back to step 310; if the
charge device non-uniformity is greater than the threshold then step 380
is initiated wherein the charge device cleaner is engaged for a
predetermined number of cycles.

[0052]FIG. 7 illustrates a flow chart wherein the controller periodically
measures the charge device non-uniformity level. When the level is
unacceptably high the controller engages the charge device cleaner for a
fixed duration and repeats until the non-uniformity level is below the
threshold. This would limit the engagement of the charge device
cleaner--only using it when needed. Step 400 indicates the start of the
process; next at step 410 is the reset print cycle count; at step 420 is
the Increment print cycle count.

[0053]At step 430 the print cycle count is compared to the cycle count
threshold; if the print cycle count is not greater than the threshold,
the process returns to step 420, if it is greater the process goes to
step 440 where the test pattern is printed under adjusted charger
settings; at step 450 the test pattern is measured with an image-based
sensor; at step 460 the charge device non-uniformity is calculated.

[0054]At step 470 the charge device non-uniformity is compared to the
non-uniformity threshold; if the non-uniformity level is not greater than
the non-uniformity threshold the process goes back to step 410; if the
non-uniformity level is greater than the non-uniformity threshold, then
step 490 is initiated wherein the charge device cleaner is engaged for a
pre-determined number of cycles then disengaged at step 480 and the
process returns to step 440 where another test pattern is printed; the
steps 460, 470, 490 are repeated until step 470 charge non-uniformity is
below the threshold value.

[0055]FIG. 8 illustrates a flow chart wherein a controller periodically
measures the charge device non-uniformity level. The controller then uses
this measurement to dynamically adjust the parameters for the charge
device cleaner. This would include parameters such as: normal force
applied to the cleaning device, frequency of engagement of the cleaning
device, amount of time left engaged, etc. The controller dynamically
adjusts said cleaner parameters thereby to maintain the contamination
level on the bias charging roll sufficiently low to prevent contamination
related print quality defects while also to minimize the degree of
cleaning action (and therefore the potential for damage to the bias
charging roll). Step 500 indicates start of the process; next at step 510
is the reset print cycle count; at step 520 is the Increment print cycle
count.

[0056]At step 530 the print cycle count is compared to the cycle count
threshold; if the print cycle count is not greater than the threshold,
the process returns to step 520, if it is greater the process goes to
step 540 where the test pattern is printed under adjusted charger
settings; at step 550 the test pattern is measured with an image-based
sensor; at step 560 the charge device non-uniformity is calculated.

[0057]At step 570, charge device cleaning parameters are calculated based
on the calculated charge device non-uniformity, and are applied to charge
device cleaning system. For example, the cleaning interval can be
determined by the following equation:

T c ( k ) = .alpha. 1 X c ( k - 1 ) + .DELTA. T
##EQU00001##

where T.sub.c(k) is the time period between cleaning cycles at sampling
instant k, .alpha. is an adjustable gain parameter, .DELTA..sub.T is a
minimum time between cleaner engagements, and X.sub.c(k-1) represents the
measured overall charger contamination level (in essence the health state
of the charge device where larger values indicate more
contamination/non-uniformity) at the prior sampling instant (k-1).

[0058]A force applied to the charge device cleaner is determined by the
following equation:

F.sub.c(k)=.beta.X.sub.c(k-1)+.DELTA..sub.F

where F.sub.c(k) is the force applied to the cleaning device during the
cleaning cycle at sampling instant k, .beta. is an adjustable gain
parameter, .DELTA..sub.F is a minimum applied force, and X.sub.c(k-1)
represents the measured overall charger contamination level (in essence
the health state of the charge device where larger values indicate more
contamination/non-uniformity) at the previous sampling instant (k-1).

[0059]It is, therefore, apparent that there has been provided a device in
accordance with the present invention which fully satisfies the aims and
advantages hereinbefore set forth.

[0060]While this invention has been described in conjunction with a
specific embodiment thereof, it is evident that many alternatives,
modifications, and variations will be apparent to those skilled in the
art. Accordingly, it is intended to embrace all such alternatives,
modifications and variations that fall within the spirit and broad scope
of the appended claims.

[0061]It will be appreciated that various of the above-disclosed and other
features and functions, or alternatives thereof, may be desirably
combined into many other different systems or applications. Also that
various presently unforeseen or unanticipated alternatives,
modifications, variations or improvements therein may be subsequently
made by those skilled in the art which are also intended to be
encompassed by the following claims. Unless specifically recited in a
claim, steps or components of claims should not be implied or imported
from the specification or any other claims as to any particular order,
number, position, size, shape, angle, color, or material.